Pulmonary vascular resistance (PVR) is an important hemodynamic variable that affects prognosis and therapy in a wide range of cardiovascular and pulmonary conditions. In the diagnosis and treatment of cardiogenic pulmonary edema, for example, pulmonary vascular resistance can be used as an indicator for the distension of small pulmonary vessels, which typically occurs in early stages of heart decompensation in response to elevated left atrial pressures. In addition to the diagnosis and treatment of pulmonary edema, pulmonary vascular resistance can also be utilized as an indicator for other conditions, including pulmonary hypertension, pulmonary embolisms, and atelectasis. Since changes in pulmonary vascular resistance often occur in the early stage of diseases such as pulmonary edema, the periodic measurement of this parameter over time may provide a useful indicator for the early detection of an acutely worsening heart failure.
A variety of different techniques have been employed for measuring pulmonary vascular resistance. In one such method disclosed in U.S. Pat. No. 7,204,798, for example, an inflatable balloon catheter is used to induce a change in volume and/or pressure within a heart chamber during systole, and then inject a fluid into the heart chamber during diastole. A sensor is then used to measure the pressure and/or volume at a location within the heart (e.g., the left ventricle or aorta), which can then be used to compute various hemodynamic parameters, including pulmonary vascular resistance. While providing a means for calculating pulmonary vascular resistance, such methods typically require the insertion of a catheter within the body, and are therefore not useful in measuring long term trends that occur over longer periods of time.